Method and Poll Control Entity for Controlling a Polling Procedure

ABSTRACT

A method and poll control entity ( 300 ) for controlling a polling procedure in a radio communication where a data transmitting node ( 302 ) transmits data ( 3:1 ) to a data receiving node ( 304 ) and sends polls to the data receiving node according to a default polling frequency. The polls require the data receiving node to send feedback ( 3:2 ) to the data transmitting node indicating whether said data has been received and decoded by the data receiving node or not. The poll control entity detects ( 3:3   a - c ) a trigger of the radio communication indicating a deviation of a feedback time which is a time period between a time of sending the poll and a time of receiving the feedback from an expected feedback time range. The poll control entity then adjusts ( 3:4 ) the polling frequency based on the detected trigger such that the deviation of the feedback time is reduced, and enforces ( 3:5 ) the adjusted polling frequency at the data transmitting node. In this way, the polling frequency can be dynamically and individually adapted to the current situation of traffic load and/or radio conditions which may influence the resulting feedback time in the radio communication, to achieve efficient communication of data and good throughput.

TECHNICAL FIELD

The present disclosure relates generally to a method and a poll controlentity for controlling a polling procedure in a radio communicationwhere a data transmitting node transmits data to a data receiving nodeand sends a poll to the data receiving node requiring the data receivingnode to send feedback indicating whether it has received and decoded thetransmitted data or not.

BACKGROUND

When data is communicated between a base station of a wirelesscommunication network and a User Equipment (UE) served by the basestation, a Radio Link Control (RLC) protocol can be applied as an RLClayer being a sub-layer of Layer 2 for handling this data communication,which has been specified by the Third Generation Partnership Project(3GPP) for Long Term Evolution (LTE) networks. The RLC layer istypically implemented by using data receiving and transmitting RLCentities in both the base station and the UE. The RLC entities areconfigured to exchange data in the form of Service Data Units (SDUs), ofa higher layer over a logical channel configured by the so-called RadioResource Control (RRC) layer thus being a higher layer above the RLClayer. On a lower layer called the Medium Access Control (MAC) layer,such logical channels are mapped to transport channels where the data iscommunicated in the form of data blocks, which communication iscontrolled by a so-called MAC-scheduler.

At RLC level, data in an SDU may further be re-arranged and segmentedinto different chunks of data, referred to as Protocol data Units(PDUs), before transmission, which are put together again at thereceiving side. A PDU may be either smaller or larger than the SDU suchthat an SDU may be divided into several smaller PDUs, or data inmultiple SDUs may be concatenated into fewer PDUs. Depending on thecommunication service used and/or current traffic situation, it may berequired that reception of the transmitted PDUs is confirmed by means ofPDU status reports sent from the data receiving RLC entity in one nodeas feedback to the data transmitting RLC entity in an opposite node.This can be applied for both downlink and uplink communication of data.

The RLC entities can be configured to apply different communicationmodes referred to as Transparent Mode (TM), Unacknowledged Mode (UM) andAcknowledged Mode (AM). In AM, PDUs are communicated and acknowledgementof correct reception of the PDUs is required and expected at the datareceiving RLC entity in the form of the above-described PDU statusreports, which is a process commonly referred to as Automatic Repeatrequest (ARO). TM and UM do not require any such status reporting andany data that has not been received properly will be missing ordiscarded at the receiving side and no retransmission of the missingdata will be requested either. Which mode to use for a session isdecided by a radio bearer mapping function at the base station,typically based on the type of service used and possibly also on theavailable resources, and the selected mode is signalled from the basestation to the UE at establishment of a radio bearer, referred to as“radio bearer setup”.

In the following description, RLC and AM will be used as an illustrativeexample, although the issues and features discussed in this disclosuremay apply to any mechanisms involving status reporting of correctlyreceived and decoded data regardless of whether the data is received inPDUs or any other format.

In FIG. 1, a base station 100 is schematically shown comprising a datareceiving RLC entity 100 a and a data transmitting RLC entity 100 b.Further, a UE 102 served by base station 100 comprises a data receivingRLC entity 102 b which can receive data, e.g. PDUs, from the datatransmitting RLC entity 100 b, and a data transmitting RLC entity 102 awhich can transmit data, e.g. PDUs, to the data receiving RLC entity 100a.

With this configuration, data in the form of PDUs may be sent on anuplink channel from the data transmitting RLC entity 102 a to the datareceiving RLC entity 100 a. In that case, corresponding PDU statusreports may be sent as feedback on an opposite downlink channel from thedata receiving RLC entity 100 a to the data transmitting RLC entity 102a, such as when the above AM is used, as shown in the figure.Correspondingly, PDUs may also be sent on a downlink channel from thedata transmitting RLC entity 100 b to the data receiving RLC entity 102b. In that case, PDU status reports may be sent on an opposite uplinkchannel from the data receiving RLC entity 102 b to the datatransmitting RLC entity 100 b.

There are some drawbacks associated with the use of status reporting,e.g. according to the above AM RLC procedure, such as delayed datadelivery, increased signaling overhead and pointless or unnecessaryre-transmissions. For example, required and expected status reports maysometimes not arrive on time or not at all to the data transmittingnode, resulting in re-transmission of data since that data has not beenacknowledged by the data receiving node, at least as perceived by thedata transmitting node. This situation may thus occur even when the datahas in fact been received and decoded successfully at the data receivingnode and an acknowledging status report has been sent but not deliveredproperly or in due time to the data transmitting node, for some reason.

In some cases, a polling procedure is applied where the datatransmitting node explicitly commands the data receiving node to send astatus report as feedback indicating whether transmitted data has beenproperly received, by adding a poll to the data transmitted to the datareceiving node. A poll may be sent by setting a bit in a header fieldattached to the transmitted data, e.g. a specific polling field in theheader is typically set to “1”. Such polls are sent according to acertain polling frequency and any data that has not been acknowledged bythe data receiver before expiry of a timer will become a candidate forretransmission.

SUMMARY

It is an object of embodiments described herein to address at least someof the problems and issues outlined above. It is possible to achievethese objects and others by using a method and a poll control entity asdefined in the attached independent claims.

According to one aspect, a method is performed by a poll control entityfor controlling a polling procedure in a radio communication where adata transmitting node transmits data to a data receiving node and sendspolls to the data receiving node according to a default pollingfrequency. The polls require the data receiving node to send feedback tothe data transmitting node indicating whether the data has been receivedand decoded by the data receiving node or not.

In this method, the poll control entity detects a trigger of the radiocommunication which trigger indicates a deviation of a feedback time ofthe radio communication from an expected feedback time range. Thefeedback time is a time period between a time of sending the poll fromthe data transmitting node and a time of receiving the feedback at thedata transmitting node. the poll control entity then adjusts the pollingfrequency based on the trigger of the radio communication such that thedeviation of the feedback time is reduced, and enforces the adjustedpolling frequency at the data transmitting node.

According to another aspect, a poll control entity is configured tocontrol a polling procedure in a radio communication where a datatransmitting node transmits data to a data receiving node and sendspolls to the data receiving node according to a default pollingfrequency. The polls require the data receiving node to send feedback tothe data transmitting node indicating whether the data has been receivedand decoded by the data receiving node or not.

The poll control entity comprises a detecting unit adapted to detect atrigger of the radio communication indicating a deviation of a feedbacktime which is a time period between a time of sending the poll and atime of receiving the feedback from an expected feedback time range. Thepoll control entity also comprises a logic unit adapted to adjust thepolling frequency based on the trigger of the radio communication suchthat the deviation of the feedback time is reduced, and an enforcingunit adapted to enforce the adjusted polling frequency at the datatransmitting node.

When using any of the above method and poll control entity, the pollingfrequency can be dynamically and individually adapted to the currentsituation of the radio communication, instead of using a fixed pollingfrequency, to enable efficient communication of data and good throughputeven when the situation changes. For example, the current traffic loadand/or radio conditions of the radio communication may influence theresulting feedback time which thus may vary in time and the pollingfrequency can be adapted accordingly. The above method and poll controlentity may thus be used to optimize or at least improve the pollingfrequency used for the radio communication between the data transmittingnode and the data receiving node. Further possible features and benefitsof this solution will become apparent from the detailed descriptionbelow.

BRIEF DESCRIPTION OF DRAWINGS

The solution will now be described in more detail by means of exemplaryembodiments and with reference to the accompanying drawings, in which:

FIG. 1 is a communication scenario illustrating transmission andacknowledgement of data between a base station and a UE, according tothe prior art.

FIG. 2 is a flow chart illustrating a procedure performed by a pollcontrol entity, according to further possible embodiments.

FIG. 2 a is a schematic diagram illustrating when different pollingfrequencies may be used, according to further possible embodiments.

FIG. 3 is a block diagram illustrating an example of a communicationscenario where a poll control entity is used, according to furtherpossible embodiments.

FIG. 4 is a flow chart illustrating a more detailed example of aprocedure performed by a poll control entity, according to furtherpossible embodiments.

FIG. 5 is a block diagram illustrating a poll control entity in moredetail when used, according to further possible embodiments.

DETAILED DESCRIPTION

In this disclosure, the term base station is used to represent a radionode of a wireless or cellular network which node is capable ofcommunicating with wireless UEs over radio channels. Depending on theterminology used, a base station may also be called NodeB, eNodeB, eNB,base transceiver station, and so forth. Further, the term UserEquipment, or UE, is used here to represent any terminal or devicecapable of communicating with the above base station and network overradio channels. Without limitation, the UE may be a handheld deviceoperated by a human user or an automatically operating device sometimesreferred to as a Machine-to-Machine (M2M) device. In the followingexamples, either of the base station and the UE may be a datatransmitting node or a data receiving node.

Briefly described, a solution is provided in a poll control entity forcontrolling a polling procedure for feedback of proper data reception ina radio communication, by introducing a more flexible use of theabove-described polling procedure chiefly using an adaptive pollingfrequency that can be adjusted in certain circumstances, instead of afixed one. The adjustable polling frequency is adjusted depending on acurrent “feedback time”, which is a time period between the time ofsending a poll from a data transmitting node and the time of receivingfeedback from a data receiving node, e.g. in the form of a status reportor the like, at the data transmitting node.

In this solution, it has been recognized that the feedback time maydeviate from an expected or “normal” feedback time range, e.g. due tothe current traffic load, resource utilization and/or radio conditions.For example, if the resulting feedback time is greater than the expectedrange, there is a risk that the feedback for transmitted data will notarrive in time, e.g. before a timer expires at the data transmittingnode, even if the data has been received and decoded properly at thedata receiving node. In that case, the data transmitting node mayprematurely decide to retransmit the data, although it is not needed. Toavoid this behavior, the poll control entity adjusts the pollingfrequency by decreasing it to counteract and reduce this deviation ofthe feedback time from the expected feedback time range, and enforcesthe adjusted polling frequency at the data transmitting node. As aresult, the latter node will allow for longer feedback time, by thepolling frequency being decreased, and unwarranted retransmissions ofdata can be avoided. The currently prevailing feedback time may beestimated and a deviation from the expected range may be detected indifferent ways which will be described in the following. First, thepolling procedure as such will be outlined in more detail.

For example, when RLC entities are used in a base station and a UE, adata transmitting RLC entity is typically able to set a poll bit in theheader of a transmitted Data PDU to prompt the opposite data receivingRLC entity to send a Status report, or “feedback” which term will beused throughout this description. The poll mechanism may also be used inother types of data transmitting nodes and is thus not limited to RLCentities. Such a poll request is normally sent with new data but ifthere is no new data or if the transmitter in the data transmitting nodeis “stalled” and cannot deliver more new data, previously transmitteddata may be re-transmitted with the poll bit set in the header of thatdata. Alternatively, the data receiving node may itself trigger a statusreport as feedback if it detects that data is missing, which is howeveroutside the scope of this solution.

If a status report indicates that a PDU has not been received properly,or if no status report has been received at all for that PDU, at leastnot before expiry of a timer, the data transmitting node is typicallyconfigured to re-transmit the PDU since it has not been acknowledged asproperly received and decoded. A PDU that has not been reported asproperly received will thus end up as a candidate for re-transmissionafter a configured amount of time, according to a timeout parameter, or“timer”, which in LTE is called “t-PollRetransmit”. The time betweenretransmissions is controlled by the timer t-PollRetransmit if no newdata can be delivered, and by either or both of optional thresholdscalled pollPDU and pollByte if new data can be delivered. A standardizedtransmitting RLC entity using AM is configured to start or restart thetimer t-PollRetransmit each time it delivers a PDU including a poll tolower layer, i.e. the timer is started at the very transmissionoccasion. The transmitting RLC entity then stops the timert-PollRetransmit upon reception of a STATUS report comprising either apositive or a negative acknowledgement.

The re-transmission may be repeated a number of times e.g. until astatus report is received as feedback from the data receiving nodeindicating that the PDU has been received and decoded properly, or untila timeout or maximum number of re-transmissions is reached. The abovepolling procedure typically used for RLC entities is also relevant andapplicable for any data transmitting node and data receiving node, whichgeneral terms will be used in the following without limitation to RLC.

It is however a problem that such polls may be transmitted to the datareceiving node too frequently when it is not able to provide feedback tothe data transmitting node in due time such that the required feedbackstarts lagging behind. The reason for this may be that the radio linkused for transmitting the data has low throughput, e.g. as a result whenthe radio link is overloaded by traffic or has poor radio conditions dueto high interference or bad coverage, resulting in delays in schedulingthe data transmissions on the radio link such that the data is receivedand decoded late at the data receiving node, if at all. The datatransmitting node may then take premature decisions to re-transmitunacknowledged data when acknowledgement is expected but not received intime, even though it is not necessary to re-transmit when the data isactually received and decoded eventually, albeit somewhat late. On theother hand, the data may be received and decoded very fast when using aradio link for the data transmission with high throughput and good radioconditions, and the feedback may also arrive faster than expected if thefeedback radio link is unproblematic. This favorable situation cannot befully exploited to increase the data throughput if a fixed pollingfrequency is used since transmission of the next data must wait for thetimer to expire.

An example of actions performed by a poll control entity for controllinga polling procedure in a radio communication will now be described withreference to the flow chart in FIG. 2. In the radio communication, adata transmitting node transmits data to a data receiving node and sendspolls to the data receiving node initially according to a defaultpolling frequency. The polls effectively indicate that the datareceiving node is required to send feedback to the data transmittingnode indicating whether the transmitted data has been received anddecoded by the data receiving node or not. The polls thus act astriggers for the data receiving node to send the feedback. As mentionedabove, the polls may be sent together with data according to the pollingfrequency and may be implemented in a polling bit or field in a headerof the data. A poll may thus be sent simply by setting a polling bit to1 or 0 in the header. In conventional polling procedures, the polls aresent with a fixed polling frequency whereas the polls can be sent withan adaptive polling frequency in the embodiments described herein asfollows.

It may be assumed that the radio communication involves datatransmission between a User Equipment (UE) and a base station of awireless communication network, either in uplink or downlink. In thatcase, the data transmitting node may be either the base station or theUE, and conversely the data receiving node may be the opposite UE orbase station, although the solution is not limited to be used by UEs andbase stations. The poll control entity is an entity that performs thefollowing actions and may be suitably implemented in the datatransmitting node or in a scheduler of a base station. The poll controlentity may be configured to accomplish any of the embodiments describedherein, e.g. by means of a processor controlled by a suitable computerprogram.

In a first shown action 200, the poll control entity detects a triggerof the radio communication indicating a deviation of a feedback timefrom an expected feedback time range. In this context, “feedback time”refers to the time period between the time of sending the poll from thedata transmitting node and the time of receiving the feedback at thedata transmitting node. It should be noted that the currently resultingfeedback time is highly dependent on the conditions regarding the linkused for transmitting the poll and also on conditions regarding theopposite link used for transmitting the feedback. Such prevailingconditions, or states, of these links may relate to current traffic loadand available resources in the network, as well as current radioconditions such as radio coverage and interference situation, to mentiona few examples.

The trigger of this action may be detected in different ways which willbe described later with reference to FIG. 3. The term “expected feedbacktime range” refers to a range of feedback time within which the feedbacktime lies during ordinary or average conditions. Alternative terms thatcould be used in this context instead of “expected” are “middle”,“average”, “intermediate”, “central” and so forth. Further, the defaultpolling frequency is deemed suitable to use when the feedback time lieswithin the expected feedback time range during more or less ordinarycircumstances. Depending on the current conditions or states of thelinks used for data and feedback, the above-mentioned deviation mayoccur when the conditions or circumstances change such that the feedbacktime either exceeds or falls below the expected feedback time range,such that the feedback time can be regarded as an “abnormal” ordivergent feedback time. Further, the feedback time may be estimated indifferent ways, and some examples will be described later below.

Having detected the trigger indicating a deviation of the feedback timefrom an expected feedback time range, the poll control entity adjuststhe polling frequency based on the detected trigger such that thedeviation of the feedback time is reduced, or counteracted, in anotheraction 202. Hence, the adjusted polling frequency is different from theso far used default polling frequency and may be adjusted by eitherdecreasing or increasing the polling frequency.

In some possible embodiments, the expected feedback time range isflanked by an upper limit and a lower limit of the expected feedbacktime range, which is illustrated in FIG. 2 a. When the current feedbacktime lies within the expected feedback time range, i.e. between theupper and lower limits, the default polling frequency is used, as shownby case A) in FIG. 2 a. In one embodiment, the polling frequency may beadjusted by decreasing the polling frequency when the detected triggerindicates that the feedback time is longer than the upper limit, asshown by case B). In another embodiment, the polling frequency may beadjusted by increasing the polling frequency when the detected triggerindicates that the feedback time is shorter than the lower limit, asshown by case C) in the figure.

Returning to FIG. 2, the poll control entity then enforces the adjustedpolling frequency at the data transmitting node, shown by a furtheraction 204, such that the adjusted polling frequency is applied by thedata transmitting node instead of the default polling frequency whentransmitting data to the data receiving node. In other words, the pollcontrol entity instructs the data transmitting node to employ, i.e.apply and use, the adjusted polling frequency instead of the defaultpolling frequency. Thereby, the polling frequency used by the datatransmitting node will be adapted to the current conditions andcircumstances, particularly relating to either or both of thecommunication links used for data and feedback, respectively. If a UE isthe data transmitting node, the adjusted polling frequency may beenforced by sending to the UE an information element called “RLC-config”comprising the parameter t-PollRetransmit. The RLC config can be sent tothe UE using a procedure called RRC Connection Reconfiguration.

For example, the solution may be used to avoid that too high pollingfrequency is used which otherwise may result in unnecessary signalingand retransmissions of data even if the data was successfully receivedand decoded in the first place, as explained above. In another example,it may be avoided that too low polling frequency is used which otherwisewould limit the data throughput to be not as high as otherwise would bepossible, as also explained above.

When the polling frequency has been adjusted and enforced, the deviationof the current feedback time from an expected feedback time range willthus be reduced, or counteracted, or even eliminated in due course,since the polling frequency has been adapted to the prevailingcircumstances, e.g. the current load on the links used for data andfeedback, respectively. After adjusting and enforcing the pollingfrequency as described above, the poll control entity may continue tomonitor, or measure, the current feedback time, e.g. with respect toanother trigger condition or the like controlling when to revert to thedefault polling frequency again. In another possible embodiment, thepoll control entity may thus instruct the data transmitting node torevert to the default polling frequency when it is detected that thefeedback time is within the expected feedback time range, i.e. hasreturned to a value between the upper and lower limits as in case A)illustrated in FIG. 2 a.

An example of a possible scenario of a radio communication where thesolution is employed, will now be described with reference to FIG. 3. Inthis example, a poll control entity 300 monitors the feedback time of aradio communication between a data transmitting node 302 and a datareceiving node 304 with respect to an expected feedback time range,which may have been defined by an upper limit and a lower limit of theexpected feedback time range, e.g. as shown in FIG. 2 a. The feedbacktime is monitored basically by watching for a trigger of the radiocommunication that indicates a deviation of the feedback time from theexpected feedback time range. In this example, three different potentialtriggers are shown, denoted first, second and third triggers,respectively, each of which can be used as the trigger of the radiocommunication to indicate the above deviation of the monitored feedbacktime from the expected feedback time range. The poll control entity 300may be configured to detect one, two or all three of them.

A first action 3:1 illustrates that the data transmitting node 302 sendsdata together with a poll to the data receiving node 304, the pollrequiring the data receiving node 304 to send feedback, e.g. in the formof status reports or the like, to the data transmitting node 302indicating whether the data has been received and decoded by the datareceiving node 304 or not. Another action 3:2 illustrates that the datareceiving node 304 sends feedback accordingly to the data transmittingnode 302, which may arrive at node 302 in time, too late, or not at all,depending on the current circumstances, e.g. the current load on thelinks used for data and feedback as described above. Actions 3:1 and 3:2are repeated, as shown by dashed arrows, in accordance with a defaultpolling frequency which is initially used by the data transmitting node302 until a new adjusted polling frequency is enforced as follows.

In either of the following alternative actions 3:3 a-c, the poll controlentity detects a trigger of the radio communication indicating adeviation of a current feedback time from an expected feedback timerange, i.e. as described for action 200 above. In one alternative action3:3 a, the trigger of the radio communication indicating the deviationcomprises the first trigger which indicates that the utilization of aresource used for the radio communication exceeds an upper utilizationlimit or falls below a lower utilization limit. The resource may be adynamically utilized resource which is a potential “bottleneck” for theradio communication in the sense that the load on the resource affectsthe feedback time. The resource may further be a shared resource whichcan be dynamically allocated and used for multiple radio communications.The resource in this context may comprise a radio resource such asamount of scheduling entities, amount of physical resource blocks and/oramount of control channel elements. In an LTE network for example, theradio resource may be associated with various channels used forcommunication according to LTE: e.g. for uplink data transmissions onthe channel called Physical Uplink Shared Channel (PUSCH), or fordownlink data transmission on the channel called Physical DownlinkShared Channel (PDSCH), or for scheduling on PUSCH or PDSCH e.g. usingthe channel called Physical Downlink Control Channel (PDCCH), or fortransmitting physical layer acknowledgements or quality information e.g.on the channels called Physical Hybrid-ARQ Indicator Channel (PHICH) andPhysical Uplink Control Channel (PUCCH).

In this case, the poll control entity 300 detects the first trigger froman entity 306 that monitors usage and performance of resources in thenetwork, which entity may be called a “Monitored System Resources” (MSR)entity 306. The MSR entity 306 is configured to identify and monitor apotential bottleneck resource and to provide the first trigger to thepoll control entity 300 when the utilization of that resource exceedsthe upper utilization limit or falls below the lower utilization limit.The first trigger may be provided to the poll control entity 300 bymeans of a suitable internal protocol depending on the implementation.

In another alternative action 3:3 b, the trigger of the radiocommunication indicating the deviation comprises the second triggerindicating that a current Round Trip Time (RTT) of the radiocommunication between the data transmitting and receiving nodes exceedsan upper RTT limit or falls below a lower RTT limit. The RTT is thusclosely related to the feedback time. In this case, the poll controlentity 300 detects the second trigger from a so-called “path proxy” 308located in a transmit-receive path between the data transmitting andreceiving nodes 302, 304, as schematically shown by a dashed line in thefigure. Likewise, the second trigger may be provided to the poll controlentity 300 by means of some internal protocol depending on theimplementation. The current feedback time may be determined by measuringat least a part of the current RTT. For example, the measured part ofthe RTT may be the time of conveying data from the data transmittingnode to the data receiving node, or the time of conveying feedback fromthe data receiving node to the data transmitting node. Further, thispart of the current RTT may depend on a delay in scheduling transmissionof at least one of the data and the feedback.

In another alternative action 3:3 c, the trigger of the radiocommunication indicating the deviation comprises the third trigger whichis received from the data transmitting node 302 when the datatransmitting node detects that the amount of pending data to betransmitted exceeds a certain data amount threshold. In other words, thethird trigger may indicate that the transmit buffer in data transmittingnode 302 comprising the pending data is congested, i.e. “choked”,because the transmission of new data from the buffer is too slow due tolong waiting time for feedback from the data receiving node 304, whichthus indicates that the current feedback time has exceeded the upperlimit of feedback time range described above. In that case, the feedbacktime should be decreased as of case B) in FIG. 2 a. On the other hand,the third trigger may indicate that the transmit buffer in node 302 isempty because the transmission of new data from the buffer is too fastwhich thus indicates that the current feedback time has fallen below thelower limit of feedback time range described above. In that case, thefeedback time should be increased as of case C) in FIG. 2 a. Also thethird trigger may be received from the data transmitting node 302 bymeans of some internal protocol depending on the implementation.

Having detected either of the first, second and third triggers describedabove, the poll control entity 300 adapts the polling frequencyaccordingly by adjusting it based on the trigger of the radiocommunication, in another action 3:4, either by decreasing or increasingthe polling frequency depending on the deviation indicated by thedetected trigger as of cases B) and C) in FIG. 2 a, respectively. Thismay be executed in practice in different ways and some possible exampleswill be described in more detail later below. A further action 3:5illustrates that the poll control entity 300 enforces the adjustedpolling frequency at the data transmitting node 302 which then appliesthe adjusted polling frequency in another action 3:6. Further actions3:7 and 3:8 illustrate that the data transmitting node 302 sends datatogether with a poll to the data receiving node 304 and receivesfeedback, while using the new adjusted polling frequency.

A more detailed example of a procedure performed by a poll controlentity for controlling a polling procedure involving a data transmittingnode and a data receiving node in a radio communication, will now bedescribed with reference to the flow chart in FIG. 4. The poll controlentity in this example may be similar to the poll control entity 300 inFIG. 3 or the poll control entity described for FIG. 2 and FIG. 2 aabove. A first action 400 illustrates that the poll control entitymonitors the radio communication for detecting a trigger of the radiocommunication indicating a deviation of a feedback time from an expectedfeedback time range. Initially, the data transmitting node 302 applies adefault polling frequency which is deemed appropriate as long as thecurrent feedback time is within the expected feedback time range.

In a next action 402, it is determined whether any detected trigger ofthe radio communication indicates that the feedback time is longer thanan upper limit, i.e. a maximum value, of the expected feedback timerange. if so, the poll control entity decreases the polling frequency inan action 404, just as in case B) of FIG. 2 a. If the current feedbacktime does not exceed the upper limit of feedback time range, it isfurther determined in an action 406 whether any detected trigger of theradio communication indicates that the current feedback time is shorterthan a lower limit, i.e. a minimum value, of the expected feedback timerange. If so, the poll control entity increases the polling frequency inan action 408, just as in case C) of FIG. 2 a. Another action 410illustrates that the poll control entity enforces the adjusted pollingfrequency of either action 404 or 408 in the data transmitting node. Ifthe outcome of both determining actions 402 and 406 is negative, i.e.the feedback time is neither longer than the upper limit nor shorterthan the lower limit, the poll control entity may return to action 400for continuing monitoring the radio communication for detecting atrigger of the radio communication, as shown by a left-sided dashedarrow.

As mentioned above, by enforcing the adjusted polling frequency, thedeviation of the feedback time from the expected feedback time range iscounteracted, i.e. reduced. After action 410 of enforcing an adjustedpolling frequency, the procedure may therefore continue by furthermonitoring the radio communication for detecting another trigger of theradio communication, in an action 412, which trigger may be called a“revert trigger”, that indicates a return of the feedback time back tothe expected feedback time range. It is thus determined in an action 414whether any detected trigger indicates that the feedback time hasreturned to fall within the expected feedback time range. If not, thepoll control entity goes back to action 412 to continue monitoring theradio communication. If it is determined in action 414 that a detectedtrigger of the radio communication, e.g. any of the above-describedfirst, second and third triggers, indicates that the feedback time iswithin the expected feedback time range, the poll control entityinstructs the data transmitting node 302 to revert to the defaultpolling frequency, as shown by another action 416, thus effectivelyenforcing the default polling frequency to be applied in the datatransmitting node 302. Thereafter, the poll control entity may return toaction 400 to continue monitoring the radio communication for detectinga trigger indicating a deviation of the feedback time from an expectedfeedback time range, as shown by a right-sided dashed arrow.

A detailed but non-limiting example of how a poll control entity can beconfigured to accomplish the above-described embodiments is illustratedby the block diagram in FIG. 5. The poll control entity 500 isconfigured to control a polling procedure in a radio communication wherea data transmitting node 502 transmits data to a data receiving node 504and sends polls to the data receiving node according to a defaultpolling frequency. As in the previous examples, the polls require thedata receiving node to send feedback to the data transmitting nodeindicating whether the data has been received and decoded by the datareceiving node or not.

The poll control entity 500 comprises a detecting unit 500 a adapted todetect a trigger of the radio communication, here denoted T1, T2 or T3referring to the above-described examples of the first, second and thirdtriggers, which trigger indicates a deviation of a feedback time, whichis the time period between the time of sending the poll and the time ofreceiving the feedback, from an expected feedback time range. Detectingthe trigger of the radio communication may be done e.g. in the mannerdescribed for action 200 or any of actions 3:3 a-c above. The pollcontrol entity 500 also comprises a logic unit 500 b adapted to adjustthe polling frequency based on the detected trigger of the radiocommunication such that the deviation of feedback time is reduced.Adjusting the polling frequency may be done e.g. in the manner describedfor action 202 or action 3:4 above. The poll control entity 500 furthercomprises an enforcing unit 500 c adapted to enforce the adjustedpolling frequency PF at the data transmitting node 502. Enforcing theadjusted polling frequency may be done e.g. in the manner described foraction 204 or action 3:5 above.

The above poll control entity 500 and its functional units 500 a-c maybe configured or adapted to operate according to various optionalembodiments. For example, when the detected trigger of the radiocommunication indicates that the feedback time is longer than an upperlimit of the expected feedback time range, the logic unit 500 b may beadapted to adjust the polling frequency by decreasing the pollingfrequency. Thereby, the indicated deviation can be reduced such that thecurrent feedback time decreases to eventually fall within the expectedfeedback time range again. On the other hand, when the detected triggerof the radio communication indicates that the feedback time is shorterthan a lower limit of the expected feedback time range, the logic unit500 b may be adapted to adjust the polling frequency by increasing thepolling frequency. Thereby, the indicated deviation can be reduced suchthat the feedback time increases to eventually fall within the expectedfeedback time range again. In another possible embodiment, the enforcingunit 500 c may be further adapted to instruct the data transmitting node502 to revert to the default polling frequency when it is detected thatthe feedback time is within the expected feedback time range.

In further possible embodiments, the detected trigger of the radiocommunication may comprise a first trigger T1 indicating that theutilization of a resource used for the radio communication exceeds anupper utilization limit or falls below a lower utilization limit. Inthat case, the detecting unit 500 a may be further adapted to receivethe first trigger T1 from an MSR entity 506.

The trigger of the radio communication may also comprise a secondtrigger T2 indicating that a current RTT of the radio communicationbetween the data transmitting and receiving nodes 502, 504 exceeds anupper RTT limit or falls below a lower RTT limit. In that case, thelogic unit 500 b may be adapted to determine the feedback time bymeasuring at least a part of the current RTT. As mentioned above, themeasured RTT part may be the time of conveying data from the datatransmitting node to the data receiving node, or the time of conveyingfeedback from the data receiving node to the data transmitting node.This part of the current RTT may further depend on a delay in schedulingtransmission of at least one of the data and the feedback. The detectingunit 500 a may be further adapted to receive the second trigger T2 froma path proxy 508 located in a transmit-receive path between the datatransmitting and receiving nodes 502, 504.

In further possible embodiments, the trigger of the radio communicationmay comprise a third trigger T3 and the detecting unit 500 a may befurther adapted to receive the third trigger from the data transmittingnode 502 when the data transmitting node detects that the amount ofpending data to be transmitted exceeds a data amount threshold.

It should be noted that FIG. 5 illustrates various functional units inthe poll control entity 500 and the skilled person is able to implementthese functional units in practice using suitable software and hardware.Thus, the solution is generally not limited to the shown structures ofthe poll control entity 500, and the functional units 500 a-c may beconfigured to operate according to any of the features described in thisdisclosure, where appropriate.

The functional units 500 a-c described above can be implemented in thepoll control entity 500 by means of program modules of a respectivecomputer program comprising code means which, when run by a processor“P” causes the poll control entity 500 to perform the above-describedactions and procedures. The processor P may comprise a single CentralProcessing Unit (CPU), or could comprise two or more processing units.For example, the processor P may include a general purposemicroprocessor, an instruction set processor and/or related chips setsand/or a special purpose microprocessor such as an Application SpecificIntegrated Circuit (ASIC). The processor P may also comprise a storagefor caching purposes.

Each computer program may be carried by a computer program product inthe poll control entity 500 in the form of a memory “M” having acomputer readable medium and being connected to the processor P. Thecomputer program product or memory M thus comprises a computer readablemedium on which the computer program is stored e.g. in the form ofcomputer program modules “m”. For example, the memory M may be a flashmemory, a Random-Access Memory (RAM), a Read-Only Memory (ROM) or anElectrically Erasable Programmable ROM (EEPROM), and the program modulesm could in alternative embodiments be distributed on different computerprogram products in the form of memories within the poll control entity500.

Some practical examples of executing the adjustment of the pollingfrequency will now be described. In a first set of examples, the pollcontrol entity may be implemented in a scheduler of a base station suchthat the adjustment is executed in a scheduler which may be a schedulerof the Medium Access Control MAC layer in a base station that houses notonly the base station MAC protocol peer but also the scheduler fordownlink and uplink transmission. In this example, user plane controllayers in the base station are configured to autonomously decrease thepolling frequency, e.g. only down to a lower minimum, or increase thepolling frequency, e.g. only up to an upper maximum. The scheduler mayindirectly determine the polling frequency that is associated to anongoing ARQ process by delaying the grant for transmission, e.g. only upto another upper maximum, or advancing the grant for transmission, e.g.only down to another lower minimum. Effectively, the number oftransmission occasions can be controlled, or “throttled”, in this waythus providing less or more opportunities, e.g. for the datatransmitting node, to transmit.

When the adjustment of polling frequency is executed in a scheduler of abase station, it may be necessary that the scheduler is capable ofdifferentiating between situations where the transmitter passes new dataand where the sending new data from the transmitter has rather stalledand is stuck in retransmission, e.g. in a situation of not receivingfeedback in time due to long feedback time. Preferably, the schedulershould not lay a hinder for the transmitter to advance its transmissionwindow, which would otherwise put an unwanted restriction to the datathroughput. A possible solution that could be used for downlinktransmission of data is for the base station to use in-band bitsincluding a “re-segmentation flag” (RF) bit, and a polling (P) bit,which bits can be sent together with data e.g. in a data packet such asan RLC PDU packet. In that case, the RLC layer transfers the RLC PDUpacket which is received at the MAC layer as a MAC SDU. The MAC layerneed not decode the RLC PDU packet in full but just extract the abovebits from the data packet to determine if the packet includes new orretransmitted data.

The RF bit may be found in the second most significant bit of each MACSDU (RLC PDU) and the P bit may be found in the next bit that follows inthe data packet. This is typically the case, regardless of whether theRLC PDU contains an AM Data (AMD) PDU or a segment of an AMD PDU, alsoregardless of whether the RLC PDU contains two or more concatenated RLCSDUs or two or more segments of RLC SDUs. If RF=1, the RLC PDU is an AMDPDU segment. This format is used when the AM RLC entity needs toretransmit a portion of an AMD PDU. Therefore, the content of such anRLC PDU is deemed to not contain new data. If P=1 in this case, it canbe assumed that the cause for polling is “Last Data Poll”, i.e. a casewhere no new RLC data can be transmitted after the transmission of theRLC PDU, e.g. due to window stalling that is when advancement of thetransmission window is restricted by long feedback time.

However, the condition RF=1; P=1 is deemed to be a necessary but notsufficient condition for detecting transmission window stalling.However, the transmission window may be stalled even if RF=0. For thisscheme to be efficient, it is required that the MAC layer candistinguish any occurrences of polling due to window stalling. In thatcase, it is possible to let the RLC entity always use RF=1 when P=1 andthe window is stalled, in the case when the cause for polling is expiryof the parameter t-PollRetransmit and no new data can be sent, e.g.regardless of whether a lower layer grant would fit some larger RLC PDU.Resources are typically strained at times of retransmissions, and wouldbe much relaxed if the RLC transmitter uses a small AMD PDU segmentinstead of a larger size of the entire AMD PDU. The energy may insteadbe used for achieving greater robustness in the physical transmission.Alternatively, the RLC layer may implement some separate additionalnotification means instead of the above-suggested in-band bits RF, P toindicate that the polling is due to window stalling.

Both of these procedures of conveying information between the RLC andMAC layers can be used also for uplink transmission. However, it isnecessary that the information arrives at appropriate time and place,and the scheduler may need to act proactively since the adjustment ofpolling frequency is made in the base station. The information that isneeded at the scheduler to distinguish the case when transmitter windowhas stalled may be conveyed in the above-described manner of using thein-band RF and P bits, or internally within the MAC layer e.g. by usinga specific MAC control element or the like. The information may also beprovided by encoded feedback over the PUCCH channel or over the PUSCHchannel. If a specific MAC control element is used for conveying theabove information, this MAC control element may be any of the presentexisting MAC control elements used over an Uplink Shared Channel(UL-SCH), such as some of the BSR formats, e.g. an LCID of 11100, 11101or 11110, but it can also be a new MAC control element, e.g. an LCID inthe range of 01011-11000.

The RLC layer monitors ARQ re-transmissions and acts according to thet-PollRetransmit parameter, also ensuring that no RLC PDU isre-transmitted beyond a limit called maxRetxThreshold. It should benoted that this scheme can still work when the adjustment of pollingfrequency is executed in the scheduler. Also, the scheme may workwithout requiring that the scheduler has any in-depth understanding ofARQ retransmission. The scheduler may need to be enabled with one ormore pre-defined limits in terms of allowed maximum and minimum pollingfrequency. It could be useful to have such polling frequency limitsarranged with some regards to the parameters signaled to the datatransmitting node, such as the parameters maxRetxThreshold;t-PollRetransmit; pollPDU; pollByte, which parameters can be used tocontrol the re-transmission and polling in the RLC layer. For example,one such limit may be an upper maximum of a relaxed, or “conservative”,polling frequency to be used during times of high traffic load and whenthere are some indication or risk of overloading some MSRs, or when anormal RTT cannot be achieved. The equationf≧f_(max)=1/(n×“t-PollRetransmit”), where n is an integer, e.g. 4, maybe used as an example of how to calculate such an upper maximum f_(max)of polling frequency.

It may also be noted that this solution may be used to avoid pollingfrequencies that are more aggressive than what is the result of using aregular t-PollRetransmit, which may be configured by the RRC layer inthe UE and by internal signaling in the serving base station. On theother hand, since the above scheme also may use a lower minimum ofpolling frequency as an overload protection, it may allow for moreaggressive setting in the RLC layer.

Alternatively, an equation which determines the adapted pollingfrequency at high traffic load may be different, e.g. it may beexponentially “decaying” as determined by the equationf≧f_(max)=1/(2^(n-1)×“t-PollRetransmit”), where n is a re-transmissioncount, i.e. an integer 1, 2, 3 . . . being the number of times where MACconsecutively detects poll due to window stalling, e.g. are-transmission count that scales with the parameter “RETX_COUNT”normally used by the RLC layer but which instead can be realized in theMAC layer.

In a second set of examples, the poll control entity may be implementedin a data transmitting node such that the adjustment of pollingfrequency is instead executed in the data transmitting node, e.g. an RLCTransmitter. In that case, the data transmitting node is in directcontrol of the polling schemes used for providing feedback from the datareceiving node to the data transmitting node. Just as in the first setof examples above, user plane control layers in the base station can beconfigured to autonomously decrease the polling frequency, e.g. down toa lower minimum, or increase the polling frequency, e.g. up to an uppermaximum.

Also here, it may be possible to transmit data in a small AMD PDUsegment (use RF=1) instead of a complete AMD PDU which is larger,whenever P=1 and the transmission window is stalled.

As in the case when the polling frequency is adjusted in a scheduler,the data transmitting node may be configured with a minimum and amaximum of polling frequency as limitations to the adjustment. But sincepacer is explicitly exposed to ARQ, the above minimum and maximum ofpolling frequency may be directly inferred from the parametert-PollRetransmit.

For example, the value conveyed by the t-PollRetransmit parameter maydetermine an upper maximum for polling frequency that occurs at timeswhen neither reporting MSRs nor measured RTTs indicate a need to reducethe polling frequency. The corresponding polling frequency is typicallyselected to maximize throughput during regular traffic hours at timeswhen the radio channel is not obstructing for RTT and when there is norisk of overloading any resources.

Another upper maximum may correspond to an adapted relaxed pollingfrequency during times of high traffic load when there is a risk ofoverloading some MSRs or when a normal RTT cannot be achieved. Theequation f≧f_(max)=1/(n×“t-PollRetransmit”), where n is an integer, e.g.4, may be used as an example of how to calculate such an upper maximumf_(max) of polling frequency.

Alternatively, an equation which determines the adapted pollingfrequency at high traffic load may be different, e.g. it may beexponentially “decaying” as determined by the equationf≧f_(max)=1/(2^(n-1)×“t-PollRetransmit”), where n is a re-transmissioncount, i.e. an integer 1, 2, 3 . . . used by the RLC layer.

A possible advantage with implementing the poll control entity in thedata transmitting node is that the polling frequency can be adjustedindividually on a per bearer basis, thus allowing for differentstrategies tailored to match different QoS levels required by differentbearers.

By using any of the above examples of adjusting the polling frequency toadapt it to the feedback time, the data transmitting node can adjust thepolling frequency to prolong or shorten the interval between consecutivere-transmissions of data, e.g. by adapting the parameterf-PollRetransmit to estimated or measured changes in the currentfeedback time. Prolonged polling intervals can be useful in some casessince it can reduce the amount of unnecessary re-transmissions of dataand polling for status reporting at high traffic load and/or bad radioconditions when only a relatively long feedback time can be achieved. Italso protects against too many unnecessary data re-transmissions and/oragainst conditions that might overload some bottleneck resource. On theother hand, shorter polling intervals can be used to receive morefrequent feedback to reduce the number of already sent packets that needto be buffered while waiting for the feedback. This can be used toincrease the data throughput in the radio communication, particularly ifbuffering capacity is a limiting factor.

For example, in a situation with high traffic load in the network, theprocessing capability typically decreases as the traffic load approachesthe network's capacity limits. In this case, it is an advantage that theload on network elements and entities can be relieved by avoiding someunnecessary re-transmissions of data by means of the embodimentsdescribed herein.

While the solution has been described with reference to specificpossible embodiments and examples, e.g. the RLC and AM procedures usedin LTE, the description is generally only intended to illustrate how thesolution may be implemented and should not be taken as limiting thescope of the solution which may be used also in other networks than LTEnetworks, where appropriate. For example, the terms “poll controlentity”, “data transmitting node”, “data receiving node”, “poll”,“trigger”, “MSR entity” and “path proxy” have been used throughout thisdescription, although any other corresponding entities, functions,and/or parameters could also be used having the features andcharacteristics described here. The solution is defined by the appendedclaims.

1. A method performed by a poll control entity for controlling a pollingprocedure in a radio communication where a data transmitting nodetransmits data to a data receiving node and sends polls to the datareceiving node according to a default polling frequency, said pollsrequiring the data receiving node to send feedback to the datatransmitting node indicating whether said data has been received anddecoded by the data receiving node or not, the method comprising:detecting a trigger of the radio communication indicating a deviation ofa feedback time which is a time period between a time of sending thepoll and a time of receiving the feedback from an expected feedback timerange, adjusting the polling frequency based on said trigger of theradio communication such that the deviation of the feedback time isreduced, and enforcing the adjusted polling frequency at the datatransmitting node.
 2. A method according to claim 1, wherein thedetected trigger of the radio communication indicates that the feedbacktime is longer than an upper limit of the expected feedback time range,and the polling frequency is adjusted by decreasing the pollingfrequency.
 3. A method according to claim 1, wherein the detectedtrigger of the radio communication indicates that the feedback time isshorter than a lower limit of the expected feedback time range, and thepolling frequency is adjusted by increasing the polling frequency.
 4. Amethod according to claim 1, wherein the data transmitting node isinstructed to revert to the default polling frequency when it isdetected that the feedback time is within the expected feedback timerange.
 5. A method according to claim 1, wherein the trigger of theradio communication comprises a first trigger indicating that theutilization of a resource used for said radio communication exceeds anupper utilization limit or falls below a lower utilization limit.
 6. Amethod according to claim 5, wherein the first trigger is received froma Monitored System Resources (MSR) entity.
 7. A method according toclaim 1, wherein the trigger of the radio communication comprises asecond trigger indicating that a current Round Trip Time (RTT) of theradio communication between the data transmitting and receiving nodesexceeds an upper RTT limit or falls below a lower RTT limit.
 8. A methodaccording to claim 7, wherein the feedback time is determined bymeasuring a part of the current RTT.
 9. A method according to claim 8,wherein said part of the current RTT depends on a delay of schedulingtransmission of at least one of the data and the feedback.
 10. A methodaccording to claim 7, wherein the second trigger is received from a pathproxy located in a transmit-receive path between the data transmittingand receiving nodes.
 11. A method according to claim 1, wherein thetrigger of the radio communication comprises a third trigger receivedfrom the data transmitting node when the data transmitting node detectsthat the amount of pending data to be transmitted exceeds a data amountthreshold.
 12. A method according to claim 1, wherein the poll controlentity is implemented in a scheduler of a base station or in said datatransmitting node.
 13. A poll control entity configured to control apolling procedure in a radio communication where a data transmittingnode transmits data to a data receiving node and sends polls to the datareceiving node according to a default polling frequency, said pollsrequiring the data receiving node to send feedback to the datatransmitting node indicating whether said data has been received anddecoded by the data receiving node or not, the poll control entitycomprising: a detecting unit adapted to detect a trigger of the radiocommunication indicating a deviation of a feedback time which is a timeperiod between a time of sending the poll and a time of receiving thefeedback from an expected feedback time range, a logic unit adapted toadjust the polling frequency based on said trigger of the radiocommunication such that the deviation of the feedback time is reduced,and an enforcing unit adapted to enforce the adjusted polling frequency(PF) at the data transmitting node.
 14. A poll control entity accordingto claim 13, wherein when the detected trigger of the radiocommunication indicates that the feedback time is longer than an upperlimit of the expected feedback time range, the logic unit is adapted toadjust the polling frequency by decreasing the polling frequency.
 15. Apoll control entity according to claim 13, wherein when the detectedtrigger of the radio communication indicates that the feedback time isshorter than a lower limit of the expected feedback time range, thelogic unit is adapted to adjust the polling frequency by increasing thepolling frequency.
 16. A poll control entity according to claim 13,wherein the enforcing unit is further adapted to instruct the datatransmitting node to revert to the default polling frequency when it isdetected that the feedback time is within the expected feedback timerange.
 17. A poll control entity according to claim 13, wherein thetrigger of the radio communication comprises a first trigger indicatingthat the utilization of a resource used for said radio communicationexceeds an upper utilization limit or falls below a lower utilizationlimit.
 18. A poll control entity according to claim 17, wherein thedetecting unit is further adapted to receive the first trigger from aMonitored System Resources (MSR) entity.
 19. A poll control entityaccording to claim 13, wherein the trigger of the radio communicationcomprises a second trigger indicating that a current Round Trip Time(RTT) of the radio communication between the data transmitting andreceiving nodes exceeds an upper RTT limit or falls below a lower RTTlimit.
 20. A poll control entity according to claim 19, wherein thelogic unit is adapted to determine the feedback time by measuring a partof the current RTT.
 21. A poll control entity according to claim 20,wherein said part of the current RTT depends on a delay of schedulingtransmission of at least one of the data and the feedback.
 22. A pollcontrol entity according to claim 19, wherein the detecting unit isfurther adapted to receive the second trigger from a path proxy locatedin a transmit-receive path between the data transmitting and receivingnodes.
 23. A poll control entity according to claim 13, wherein thetrigger of the radio communication comprises a third trigger and thedetecting unit is further adapted to receive the third trigger from thedata transmitting node when the data transmitting node detects that theamount of pending data to be transmitted exceeds a data amountthreshold.
 24. A poll control entity according to claim 13, wherein thepoll control entity is implemented in a scheduler of a base station orin said data transmitting node.